Internal combustion engines



Sept. 10, 1968 J. H. WOOD ETAL 3,400,690

INTERNAL COMBUSTION ENGINES Filed Sept. 15, 1966 United States Patent ABSTRACT OF THE DISCLOSURE A method of reducing the gas loading on the piston to crankshaft running gear of multi-cylinder internal combustion engines by using an inert gas at high pressure in the crankcase to offset the gas working pressure in the engine cylinders.

This invention relates to internal combustion engines of the reciprocating single-acting type e.g. two or four stroke petrol or diesel engines, employing a carburettor or fuel injection mechanism.

In the previously proposed diesel engines which are pressure charged, very high working cylinder gas pressures exist which exert a considerable loading on the running gear of the engine, e.-g. .pistons, piston rings, gudgeon pins, small end bearings, connecting rods, large end bearings, crankshaft and main bearings. This increased loading on the running gear has meant that the components of the gear have to be strengthened either by manufacturing the components from stronger materials or by increasing the size of the components. This results in a considerable rise in the cost of production of the engine and in the latter case has an additional disadvantage in that the size of the engine is increased.

An object of the present invention is to provide a reciprocating internal combustion engine in which relatively high gas pressures can be employed in the cylinders without the disadvantage of increased loading on the running gear of the engine... 7

According to the present invention there is provided a method of decreasing the loading on the running gear of a multi-cylinder internal combustion engine of the reciprocating type comprising introducing into the crankcase an inert gas at a pressure which is sufficiently high to offset substantially the average gas working pressure in the engine cylinders and thereby effectively reduce the loading on the running gear.

Preferably the inert gas is maintained at a pressure substantially equal to the average gas working pressure in the cylinders of the engine.

It is desirable that the pressure within the crankcase be maintained by introducing more gas as is necessary to compensate for unavoidable leakages.

The general principles underlying the present invention will now be described with reference to the accompanying drawings, in which:

FIG. 1 is a graph showing the work cycle of a conventional reciprocating internal combustion engine, and FIG. 2 is a graph showing the work cycle of a reciprocating internal combustion engine according to the present in- 'vention.

Referring to the drawing, Vs is the swept volume of 3,400,690 Patented Sept. 10, 1968 "Ice the engine, V0 is the clearance volume, Pg is the gas pressure on the piston, the dotted line represents the crankcase pressure, and the work cycle of the engine is A to B to A in the direction of the arrows.

In the majority of modern reciprocating internal combustion engines the crankcase pressure is just below atmospheric pressure and the net work to the piston is represented by the area within the curves, i.e. by crossh-atched area 3 in FIG. 1. The maximum pressure loading on the pistons, small ends, connecting rods, large ends and main bearings (i.e. the transmission) is pro portional to AP in FIG. 1.

The present invention proposes the preservation of the crankcase of a multi-cylinder single acting engine crankcase, the dotted line in FIG. 2 indicating the crankcase pressure in this case.

The nett or indicated work is represented by the area within the curves, i.e. by the cross-hatched area 4, and the pressure loading AP is smaller than in the work cycle shown in FIG. 1, even though the gas pressure in the combustion chamber reaches a higher value.

An embodiment of the invention will now be described by way of example.

A reciprocating internal combustion engine of generally known construction and which may be powered by petrol or diesel fuel, comprises a cylinder into which fuel is fed to be exploded by either spark or pressure ignition to effect movement in the customary manner of an associated piston with its movable accessories consisting of piston rings, gudgeon pin, small end bearing, connecting rod and large end bearing.The large end bearing is carried in known manner by a crankshaft mounted in main bearings and located within a crankcase containing lube oil. Within the crankcase is contained a gas which is chemically inert to the crankcase material and its contents.

The gas, which can be nitrogen, carbon dioxide or dry exhaust gas is maintained at a pressure substantially equal to the average gas working pressure in the cylinders of the engine. The gas in the crankcase is not consumed during the working cycles of the engine but the pressure is merely maintained at intervals by introducing more gas to make up for that lost due to unavoidable leakages from the crankcase.

The crankcase of the engine and the seals in the crankcase are designed to withstand the excess pressure within the crankcase.

The present invention provides a means whereby the pressure differential existing between the engine cylinder and the crankcase tends to be decreased thereby reducing the loading on the running gear of the engine. In this way the engine can cope with the very high working cylinder gas pressures which are involved, for example, in pressurecharged diesel engines without reinforcement of the en gine running gear.

What we claim is:

1. A method of decreasing the loading on the running gear of a multi-cylinder internal combustion engine of the reciprocating type comprising introducing into the crankcase an inert gas at a pressure which is sufficiently high to offset substantially the average gas working pressure in the engine cylinders and thereby effectively reduce the loading on the running gear.

2. A method as claimed in claim- 1 in which the inert gas is maintained at a pressure substantially equal to 3 v 1 the average gas working pressure in the cylinders of the 7 1,389,017 8/1921 :Stewart 123-'192 engine- 2,429,732 10/1947 Roos 123-1 3. A method as claimed in claim 1 in which the 2782 773 2/1957 Stone 123 198 pressure within the crankcase is maintained by introducing more gas as is necessary to compensate for unavoid- 5 FOREIGN PATENTS able leakages.

References Cited 1,127,696 8/1956 France.

UNITED STATES PATENTS a 820,626 5/1906 Crowley WENDELL E BURNS, Pnmww Ex mmer 

